Lubricating oils by hydrocracking and solvent extraction

ABSTRACT

LUBRICATING OILS OF HIGH VISCOSITY INDES ARE PREPARED BY HYDROCRACKING AN APHALT-CONTAINING VACUUM RESIDUUM, RECOVERING A LUBE OIL FRACTION FROM THE PRODUCT AND SOLVENT REFINING THE RECOVERED LUBE OIL FRACTION.

United States Patent 3,766,055 LUBRICATING OILS BY HYDROCRACKING AND SOLVENT EXTRACTION Billy H. Cummins and William B. Ashton, Nederlaud, and James A. Brasher and John D. Askew, Jr., Groves, Tex., assignors to Texaco Inc., New York, N.Y.

No Drawing. Continuation of abandoned application Ser. No. 827,064, May 22, 1969. This application July 19, 1971, Ser. No. 164,028

Int. Cl. Cg 37/04 US. Cl. 208-92 9 Claims ABSTRACT THE DISCLOSURE Lubricating oils of high viscosity index are prepared by hydrocracking an asphalt-containing vacuum residuum, recovering a lube oil fraction from'the product and solvent refining the recovered lube oil fraction.

This application is a continuation of Ser. No. 827,064, filed May 22, 1969, now abandoned.

This invention relates to the refining of lubricating oils. More particularly, it is concerned with the production of high viscosity index lubricating oils in good yields from residua while dispensing with the conventional deasphalting step. In one of its more specific embodiments a crude oil having a Watson Characterization Factor of at least 11.5 is vacuum distilled, the vacuum residuum is hydrocracked, the hydrocracked product is solvent refined and the resulting rafiinate is dewaxed to produce a high quality lube oil.

In the conventional refining of petroleum, the crude oil is ordinarily subjected to distillation at atmospheric pressure to remove naphtha, kerosene and light and heavy atmospheric gas oils as distillate. The remaining atmospheric residuum or reduced crude as it is sometimes called is then subjected to distillation under reduced pressure generally referred to as vacuum distillation to yield as distillate vacuum gas oils and the lighter lubricating oil cuts. The bottoms termed vacuum residuum is then solvent deasphalted by treatment with a low molecular weight hydrocarbon deasphalting agent such as propane or butane to produce a deasphalted residuum from which heavier grade lubricating oils are recovered either by vacuum distillation or by solvent fractionation. Customarily the lubricating oils are refined either by severe hydrogenation or by the use of a preferential solvent for aromatics to increase the viscosity index and are then dewaxed to reduce the pour point.

For the production of higher yields of lighter grade lubricating oils it has been proposed to hydrocrack the oil obtained by the deasphalting of the vacuum residuum. This has to a large extent proven satisfactory. For example when a vacuum residuum obtained from a blend of various crudes is deasphalted and the deasphalted oil is hydrocracked, the lubricating oil cut at a viscosity level of about 450 SUS/ 100 F. has a high viscosity index e.g. 100-120 whereas a raw lubricating oil distillate obtained from the same crude cut to the same viscosity level has an intermediate viscosity index e.g. 75-95 and a similar cut from the hydrocracked residuum has a low viscosity index.

i In the processing of the lubricating oils in this manner, the deasphalting step has been considered essential. When a vacuum residuum such as that described above is subjected to hydrocracking without preliminary deasphalting, the viscosity index of the lube oil out at thecorresponding viscosity level is about 55-56. Thus while hydrocracking is ordinarily expected to produce an increase in the viscosity index of a lubricating oil, it is apparent that when the lubricating oil contains asphaltic materials then the 3,760,55 Patented Oct. 16, 1973 ice opposite is true. The above sequence shows that the hydrocracking of a vacuum residuum produces a lubricating oil cut at a designated viscosity level which has a viscosity index even lower than the corresponding oil of the virgin distillate.

We have now discovered a process for the production of lubricating oils of high viscosity index in good yields. According to our process a vacuum residuum without preliminary deasphalting is subjected to hydrocracking at a temperature between about 650 and 900 F., a pressure between about 500 and 5000 p.s.i.g., a space velocity (volumes of oil per volume of catalyst per hour) between about 0.1 and 10 and a hydrogen rate of 1000 to 10,000 s.c.f.b. (standard cubic feet per barrel of charge) in the presence of hydrocracking catalyst, a lubricating oil fraction is recovered from the hydrocracking zone efiluent, the recovered lubricating oil fraction is subjected to solvent refining with a solvent having an aflinity for aromatic hydrocarbons to improve the viscosity index and the solvent refined material is then dewaxed to produce a lubricating oil of reduced pour point.

The vacuum residua used in the process of our invention may be obtained from any suitable source. It will be appreciated that some crudes are better than others as a source of lubricating oils. Some properties which make for good lubricating oil source crude oils are the presence of high viscosity index hydrocarbons in the lube oil fraction, a high yield of lubricating oil from solvent refining and a high yield of SAE 20 grade oil relative to the heavier or residual fractions since SAE 20 grade oil requirements are in greater commercial demand. Suitable crudes include those having a Watson Characterization Factor of at least 11.5 and preferably 11.8 or higher. Examples of such crudes are Lafitte, Paradis, North Texas Special, North Texas Regula and West Texas-New Mexico Sour.

The reaction conditions for the hydrocracking of the vacuum residuum may be varied depending on the amount of hydrocracking desired and on the charge stock. Typical reaction conditions include a temperature of about 650- 900 F., preferably 750-850 F. The pressure may range between about 500 and 5000 p.s.i.g., a preferred range being from 1000 to 2500 p.s.i.g. Space velocities may vary between about 0.1 and 10.0 v./v./hr. with a preferred range being 0.3-1.5. Hydrogen rates of from 1000-10,000 s.c.f.b. have been found satisfactor although rates of 3000-10,000 s.c.f.b. are preferred.

Hydrogen from any suitable source such as electrolytic hydrogen, hydrogen obtained from the partial combustion of hydrocarbonaceous material followed by shift conversion and purification or catalytic reformer by-prodnct hydrogen may be used. The hydrogen should have a purity of between about 50 and 100% although hydrogen purities of at least volume percent are preferred.

The catalyst for the hydrocracking step preferably comprises a compound of a Group VI metal such as molybdenum, chromium or tungsten associated with a compound of a Group VIII metal such as cobalt, iron or nickel. The catalyst may be charged to the reactor in oxide form in which case it can be expected that some reduction and some sulfidation take place during the course of the process so that after being on stream for some time the catalyst is probably a mixture of the metal, the metal sulfide and perhaps the oxide. If desired, the catalyst after being charged to the reactor but prior to the institution of the on stream period may be converted at least in part to the sulfide form for example by contact with a gas such as a mixture of hydrogen and a sulfiding agent, e.g. hydrogen sulfide, methyl mercaptan or carbon disulfide. The Group VIII metal may be present in an amount varying from 1 to 20% by weight of the total catalyst composite, preferably 2-10% and the Group VI metal may be present in an amount ranging from about 5-40%, preferably 720%.

The metal components may be supported on a refractory inorganic oxide material such as decationized zeolite, alumina, zirconia or magnesia associated with from about 230% silica and mixtures thereof optionally promoted with an acidic material such as boron oxide or a halogen. In a preferred embodiment the support is a mixture of alumina and silica.

The catalyst should have a surface area of at least 100 m. /g., preferably 130-250 m. g. and a pore volume of at least 0.3 cc./ g. The upper limit of the surface area and pore volume is governed by the hardness and ruggedness of the catalyst. The catalyst may be used in the form of a slurry, a fixed bed or a fluidized bed but as a practical matter, for commercial installation where the catalyst is used as fixed beds in units capable of processing several thousand barrels of charge per day, the surface area preferably does not exceed about 400 m. /g. and the pore volume preferably does not exceed about 0.8 cc./g.

The preferred catalyst may be prepared by any of the methods well known in the art, such as by impregnating the support with a solution of a salt of one of the metals, filtering, drying and then impregnating with a solution of a salt of the other metal, filtering, drying and calcining in a manner well known in the :art. Advantageously, the support prior to the impregnations has a surface area and pore volume slightly in excess of the desired properties of the finished catalyst as the surface area and pore volume are to some extent reduced during the preparation of the catalyst.

The efiluent from the hydrocracker is cooled and hydrogen-rich gas separated therefrom and recycled to the hydrocracking zone. Advantageously, the hydrogen rich stream is scrubbed with water to remove any ammonia contained therein or a portion thereof may be bled from the system to prevent the build-up of ammonia and/or low molecular weight hydrocarbons. Hydrogen is added to the recycle stream to replace that consumed in the hydrocracking reaction and if necessary to replace any hydrogen purged from the system. Lubricating oil fractions are recovered from the balance of the hydrocracker effluent by distillation, if necessary, at reduced pressure.

The hydrocracked oil is then subjected to batch or continuous solvent refining with a solvent having an affinity for aromatic hydrocarbons which is at most only partially soluble in the oil so that two phases can be formed, an extract phase containing solvent and dissolved aromatics and a raflinate phase. Suitable solvents are furfural, nitrobenzene, dimethyl formamide, liquid S and the like. Solvents are generally used at dosages of 100-700% and at temperatures between 120 and 250 F., preferred conditions being dosages of 100-300% and temperatures between 120 and 180 F. A particularly suitable solvent is N-methyl 2-pyrrolidone which can be used at a lower temperature and lower dosage than the other solvents mentioned above. In addition N-methyl pyrrolidone is preferred because of its chemical stability and its ability to produce even lighter colored refined oils.

To improve the pour point of the oil the raffinate recovered from the solvent refining after removal of residual solvent is dewaxed. Dewaxing is generally effected by contacting the raffinate from the solvent extraction with a preferential solvent to separate waxy from nonwaxy material. Suitable solvents comprise a mixture of an aromatic hydrocarbon such as benzene, toluene or xylene with an alkyl ketone containing from 3 to 8 carbon atoms such as acetone, methyl ethyl ketone, methyl propyl ketone and the like. Depending on the desired pour point and miscibility characteristics, the solvent may contain from about 40-60% ketone and 60-40% aromatic hydrocarbon. Dilution is generally in the range of 1.5- parts of solvent per part of oil. The mixture is chilled, filtered and washed, the filtering temperature being selected in accordance with the desired pour point. Gen- 4 erally, the filtering is carried out at a temperature of from +20 F. to 30 F.

An added feature of our invention is that it lends additional commercial advantage to the hydrocracking of vacuum residua for the production of lighter materials such as motor and jet fuels. Heretofore, such a procedure was not considered too satisfactory because of the low quality lube oil stock which was produced. However, now this lube oil fraction can unexpectedly be converted into an improved lube oil of high viscosity index by conventional solvent refining to obtain in some instances an unusually large increase in the viscosity index of over 60 units, a much greater increase than is obtained by solvent refining in conventional lube oil processing.

The following examples are given for illustrative purposes only.

EXAMPLE I TABLE I Oil Number 1 2 3 Viscosity indox Pour point, F

The oil obtained by hydrocracking the deasphalted vacuum residumm has a high viscosity index, as expected, higher than the viscosity index of the virgin lube distillate whereas the viscosity index of the oil obtained by hydrocracking the vacuum residuum is quite low, lower, in fact, than that of the virgin distillate.

EXAMPLE H In this example, charge stock 4 is the product obtained by hydrocracking a West Texas-New Mexico Sour vacuum residuum at a temperature of 802 F., a pressure of 2000 p.s.i.g., a space velocity of 0.45 v./v./hr. using hydrogen of 88 volume percent purity at a rate of 7180 s.c.f.b. over a fixed bed of a sulfided catalyst having the following characteristics:

TABLE H Surface area, mF/g. Pore volume, cc./g 0.47 Ni, wt. percent 5.6 W, wt. percent 10.9 B 0 wt. percent 10.6 SiO wt. percent Trace A1 0 wt. percent Remainder and subjecting the product to vacuum distillation. Charge stock 5 is a raw distillate from the same crude cut to approximately the same viscosity at 210 F. as the charge stock 4 cut from the hydrocracked vacuum residuum. Data on the charge stocks and products appear below.

TABLE III Charge stock 4 5 Refractive index at 70 C l. 6030 1. 4730 Vlxcosity, SUS/i00 F 279 138 Viscosity, SUS/2l0 F 44. 5 41. 6 Viscosity index 67 77 Furfural extraction:

Dosage, volume percent. 350 350 Temperature, 180 180 Yield basis RI, volume percent 54 63 Waxy refined oil tests:

R1 at 70 C 1. 4614 1. 452A Viscosity, BUS/210 F- 48. 7 40. 5

Viscosity index 120 117 EXAMPLE III This example also shows that lubricating oils which are equal in quality to oil obtained by solvent refining a virgin distillate can be prepared by hydrocracking a vacuum residuum and solvent refining the recovered lubricating oil using batch type extraction. Charge stock 6 represents a virgin distillate and charge stock 7 an oil recovered from a vacuum residuum hydrocracked at the same conditions as in Example II. Data on the characteristics of EXAMPLE IV This example is similar to Example III except that the furfural extraction conditions are changed to the extent indicated in Table V below.

TABLE V Charge stock 6 7 Furiural refining conditions:

Solvent dosage volume percent 1,400 1, 400 Temperature, F. 180 180 Waxy product tests:

Viscosity, SUS/210 F 40. 1 Viscosity index Example I shows that a high quality lubricating oil can be prepared from a vacuum residuum by removing the asphalt and hydrocracking the deasphalted residuum. Example I also shows that although the oil produced by hydrocracking the deasphalted residuum is superior to the virgin distillate oil, the lube oil cut recovered from a hydrocracked residuum (which has not been deasphalted) is decidedly inferior to the virgin distillate oil. However, Examples II, III and IV show that the lube oil recovered from the hydrocracked vacuum residuum has such a tremendous solvent refining response that it is essentially equivalent to a solvent refined virgin distillate oil. As can be seen from Table III, the virgin oil response to furfural refining is 40 units in the viscosity index whereas in the solvent-refined hydrocracked vacuum residuum oil the response is 53 units. Similarly from Table IV the response is 34 and 57 respectively and in Table V 46 and 66 respectively.

Although we do not wish to be bound by the following theory, it would seem that due to the presence of the asphaltic molecules in the vacuum residuum, the polycyclic aromatics are cracked to lube oil range aromatic compounds which prevent a high viscosity index being achieved but the balance of the residuum molecules are converted to high viscosity index molecules. Since the lube fraction from the hydrocracked asphalt-containing vacuum residuum contains both extremely high VI (parafiinic) molecules and very low VI (aromatic) molecules, it has an excellent response to solvent refining. Although the hydrocracked material from the asphaltic vacuum residuum is more aromatic than raw lube stock from the same crude, there are very high VI molecules present which upon subsequent solvent refining result in base oils having a viscosity index at least equal to that obtained by conventional processing of raw lube distillates obtained from the same crude.

While the invention has been described with respect to several specific embodiments, those skilled in the art will appreciate that various modifications as set forth above may be made without departing from the spirit and scope of the invention.

We claim:

1. A process for the production of lubricating oils which comprises distilling an asphaltic crude petroleum oil under subatmospheric pressure to yield as distillate a virgin lubricating oil and as still residue an asphalt containing vacuum residuum, introducing into a hydrocracking zone a feed consisting essentially of hydrogen and said vacuum residuum which has not been deasphalted, hydrocracking said asphalt-containing vacuum residuum in the presence of a hydrocracking catalyst, recovering from the hydrocracked product a fraction boiling in the lubricating oil range having a viscosity index below that of a raw distillate fraction obtained from said virgin lubricating oil having a viscosity SUS at 210 F. substantially the same as that of said hydrocracked fraction, and increasing the viscosity index of said hydrocracked fraction boiling in the lubricating oil range at least 40 units by subjecting said fraction to solvent refining to produce a lubricating oil of improved viscosity index.

2. The process of claim 1 in which the lubricating oil of improved viscosity index is subjected to a dewaxing treatment.

3. The process of claim 1 in which the hydrocracking catalyst comprises a Group VIII metal or compound thereof.

4. The process of claim 3 in which the hydrocracking catalyst comprises a Group VI metal or compound thereof.

5. The process of claim 3 in which the hydrocracking catalyst comprises nickel and molybdenum.

6. The process of claim 3 in which the hydrocracking catalyst has a pore volume of at least 0.3 cc./g., a surface area of at least mF/g. and a silica content of at least 2.0 weight percent.

7. The process of claim 1 in which the dosage of solvent to lubricating oil in the solvent refining step does not exceed about 700%.

8. The process of claim 7 in which the dosage is between 350 and 700 volume percent, inclusive.

9. The process of claim 1 in which the solvent is N-methyl-Z-pyrrolidone.

References Cited UNITED STATES PATENTS 3,308,055 3/1967 Kozlowski 208-18 3,240,696 3/1966 Halik et al. 208-l8 3,562,145 2/1971 Franz et al 208-48 3,414,506 12/1968 Campagne 208l8 3,463,724 8/ 1969 Langlois et a]. 20818 OTHER REFERENCES Purdy Petroleum, p. 142, McGraw-Hill, New York (1958).

HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208-18, 96 

